Simvastatin in Secondary Progressive Multiple Sclerosis

Approximately 60% of those affected with relapsing-remitting MS (RRMS) enter a SPMS stage after a median interval of 10 to 15 years, where disability accumulates gradually in the absence of relapses. A smaller proportion (15%), run a progressive course from onset (primary progressive (PP) MS). The progressive, "neurodegenerative" component of MS, rather than the clinical deficit resulting from incomplete recovery from each relapse in RRMS, is the dominant cause of long-term disability. Whilst over ten therapies are now licensed for RRMS, no treatment strategies, with the exception of a recent study by the investigators, have succeeded in slowing the progression of this later debilitating stage.

Optic neuritis, inflammation of the optic nerve, is a common event associated with MS resulting in 27% of subjects with residual visual impairment. The impact of damage arising from an inflammatory lesion in the optic nerve can be visualised using optical coherence tomography (OCT) as a reduction in both ganglion cell layer and retinal nerve fibre layer thickness. However it is increasingly being appreciated that a number of other inflammatory and neurodegenerative changes occur in the retina of MS patients. These retinal changes, reflecting both the disease and its level of activity, have highlighted its potential as a surrogate outcome measure to study preservation of neuronal and/or vascular structure/function after an inflammatory event or as the disease progresses.

During the last two decades there have been significant advances in the understanding of MS leading to treatment for the RRMS phase. Despite this, there has been a failure to find an effective treatment for progression and this remains a major unmet need, as highlighted by the International Progressive MS Alliance. The many challenges of progressive studies including optimal design, sensitive outcomes, suitable length and subject numbers are gradually being overcome by the MS community, but as yet extending the anti-inflammatory approach that has been effective in RRMS has not borne fruit in SPMS. Indeed the failure of the recent PPMS trial using fingolimod makes the success of simvastatin in the SPMS study all the more exciting, especially as the extensive systemic immunological assessment in this latter study revealed no impact on immune status. The real success of this simvastatin phase II study may be that it initiates novel avenues of investigation driven by the wide-ranging and well-characterised effects statins have on the body as well as a prelude to a definitive phase III trial. This premise underpins the research strategy.

Preclinical work has focused on the role played by the vascular barriers (the blood-brain and blood retinal barriers) in the inflammatory process and in particular how they support leukocyte traffic to the central nervous system (CNS). This research, along with that of others, led to the identification and characterisation of endothelial cell (EC) signalling processes that facilitate leukocyte diapedesis and activate pro-inflammatory responses. The investigators found that a key central regulator of the EC signalling pathway supporting leukocyte diapedesis was the small GTPase Rho, and this led to investigating whether small GTPases could be targeted pharmacologically to reduce aberrant leukocyte migration into the brain and retina. Since small GTPases require posttranslational lipid modification (prenylation) to become functional, the investigators tested whether inhibition of Rho prenylation with prenyl transferase inhibitors (PTIs) affects lymphocyte migration. Treatment of brain endothelial cell monolayers in vitro, or animals induced for experimental autoimmune encephalomyelitis (EAE, the animal model of MS), resulted in inhibition of lymphocyte migration and attenuation of the disease respectively.

Since the isoprenoids used for post-translational prenylation of small GTPases are derived from the cholesterol synthesis pathway, the investigators next investigated whether HMGCoA reductase inhibitors (statins) were also able to significantly inhibit Rho activity and reduce the severity of brain and retinal inflammatory disease. This research revealed that statins effectively reduced Rho prenylation and attenuated disease in experimentally induced models of MS and posterior uveitis. Whilst the investigators were able to demonstrate that one of the effects of statin treatment was to modify endothelia cell function and inhibit transendothelial migration of leukocytes, it is clear from many other experimental studies that efficacy may also be due to effects on other cell types such as immune cells.

Indeed, it is now widely recognised that statins have anti-inflammatory properties that operate independently of their cholesterol lowering effect. Accordingly, statins have been shown to inhibit MHC class II restricted Ag presentation, attenuate antigen-presenting cell maturation and down-regulate T cell activation and proliferation. Of those T cells that proliferate, statins induce a shift from a proinflammatory Th1 to a regulatory Th2 phenotype. In addition, statins block adhesion molecule expression and their interactions, inhibit the production of chemokines and their receptors, and reduce the secretion of matrix metalloproteinases. Activation of the transcription factor NFκB, an important activator of pro-inflammatory mediators, is also inhibited by statins, alongside a concomitant upregulation of endothelial cell protective genes. Finally, it has been shown that endothelial nitric oxide synthase (eNOS) activity is enhanced, whilst inducible NOS (iNOS) is inhibited.

This remarkable pleiotropic capacity for modulating the immune system and inflammation has prompted the clinical testing of statins for the treatment of RRMS and other inflammatory diseases. In one such study in 30 patients with RRMS, simvastatin (80mg) taken over 6 months reduced the number of brain lesions by 40%, although no change in disability scores was observed over this short study period. Other studies, however, have failed to demonstrate any significant clinical improvement in RRMS following statin treatment alone or in combination with other disease modifying drugs. Nevertheless, it should be noted that none of the studies so far have been sufficiently powered, rendering definitive conclusions impossible.

Whilst there is a clear-cut rationale for using statins for the treatment of RRMS, in SPMS there is less obvious justification, as disease progression in the absence of new plaque formation is thought to be due predominantly to neurodegeneration (or neuronal loss). This results from several mechanisms, including microglia activation, chronic oxidative injury, accumulation of mitochondrial damage in axons, and age-related iron accumulation in the human brain. Whereas large scale inflammatory lesions rarely occur at this stage of the disease, inflammation is prominent in progressive MS, where it is found throughout the grey and white matter, and in the meninges, with its most severe form being represented by the ectopic follicles that contribute to grey matter damage. This suggested that given their Immunomodulatory / anti-inflammatory actions, statins might still provide some benefit in SPMS. Nonetheless, neuronal loss is regarded as the key pathological feature, which raised the question whether statins also possess neuroprotective properties. Several lines of evidence suggest this may be the case.

Firstly, statins are increasingly seen as vasculoprotective with a capacity to improve vascular perfusion and maintain/enhance blood vessel function thus protecting against long-term chronic hypoxic damage. This is germane given the growing evidence that dysfunctional/reduced blood flow in MS may predispose the tissue to damage resulting in neuronal cell dysfunction and ultimately cell death. Such beneficial effects on microvascular perfusion may be mediated through statins enhancing eNOS activation and inhibiting endothelin-1.

Secondly, there are reports that statins may also be neuroprotective through reducing free radical damage either by improving blood flow and reducing hypoxia-mediated reactive oxygen species (ROS) production, or through direct inhibition of cytotoxic pathways. In the latter case, statins may protect neuroparenchymal cells via inhibition of iNOS in activated microglia and astrocytes, resulting in attenuated cytotoxic damage to neurons and oligodendrocytes. Furthermore, statins may also exert a neuroprotective effect by preventing glutamate-mediated excitotoxicity.

Together these data provided a compelling rationale for testing the potential therapeutic effect of statins in SPMS. In 2008, the investigators therefore embarked on a two-year double-blind, controlled trial of 140 patients, randomising them to either 80mg of simvastatin or placebo. The recently published results of this trial showed that brain atrophy was reduced by over 40% alongside a similar favourable effect on two major disability outcome measures. This is the first evidence of a drug having a beneficial effect on SPMS disease progression. Surprisingly, however, and contrary to expectations, the investigators did not identify any modulation of the immune system, raising the critical question of the mechanism of statin action.

It is the hypothesis, therefore, that the neuroprotective effects of statins in SPMS are mediated by stimulating enhanced microvascular perfusion and/or by inhibition of oxidative damage/neurotoxicity. This study will test this hypothesis.

There are no current treatments for SPMS. Given the investigators demonstrated that simvastatin was beneficial in a phase II trial but were unable to elucidate any mechanism, it is important to try and understand the mechanism of action to develop further therapies.

The investigators will investigate the impact of high dose simvastatin (80mg/day) on cerebral and retinal blood perfusion and vascular structure/function, brain neuroaxonal density and glutamate excitotoxicity in SPMS. In addition, various systemic parameters will be evaluated to determine the effect of high dose statin treatment on immune function, oxidative damage and vascular barrier function.

Simvastatin is being used outside of its posology and method of administration. The previous phase two trial found simvastatin was safe up to the maximum dose of 80 mg/day given as a single dose in the evening. Based on the recommendations of the SPC and previous studies, the proposed use of 80mg of Simvastatin will, therefore, be used for this study.